Among the many pathways to improving on today’s energy storage technologies, the addition of conductive ‘filler’ materials to electrodes promises better rate capability, conductivity and overall battery performance.
“Although a variety of conductive fillers have been extensively developed,” explain scientists led by the University of Texas at Austin (UTA), “the understanding of how the geometry and dimensionality of these fillers affect the electrode conductivity, architecture, and ultimately the electrochemical performance in high-energy storage systems, is still insufficient.”
The group conducted experiments with three different conductive carbon materials, to determine which offered the best performance. Varying amounts of single-walled carbon nanotubes, graphene nanosheets and ‘Super P’ – a type of carbon black particle already commonly used as a conductive filler in lithium-ion batteries – were added to a nickel-cobalt-manganese (NCM) cathode.
These cathodes were then measured using various spectroscopic and electrochemical characterization techniques. Full results are published in the paper Unveiling the dimensionality effect of conductive fillers in thick battery electrodes for high-energy storage systems, published in Applied Physics Reviews.
Single-walled carbon nanotubes (SWCNTs) were shown to be the best performing additive. The group observed that the nanotubes formed a conductive coating around the NCM particles, and also formed interconnected networks between the NCM particles. Graphene nanosheets had a similar effect but formed less uniform structures.
The best of the SWCNT electrodes showed a capacity of 142 milliamp-hours per gram (mAh/g) at a charge rate of 0.2 C, falling to 101 mAh/g when the rate increased to 2 C. The group also found that as little as 0.16% by weight of SWCNTs was enough to ensure good conductivity. “When an electrically conductive filler is added to an insulating matrix,” explains UTA’s Guihua Yu, “significant increases in conductivity will occur once the first conducting pathway through the composite is formed.”
The group says its findings suggest that integration of SWCNTs in this way could facilitate better ion and charge transfers, leading to better-performing batteries especially at high discharge rates. And overall, the improved understanding of conductive filler behavior could open new doors in the design of high energy/power density electrodes.
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